In the past two grant cycles, we examined schedules of reinforcement in contingency management (CM) treatments, with the goal of identifying the most efficacious and least costly CM approach. We found that voucher and prize CM are equally efficacious in reducing cocaine use when magnitude of reinforcement is equal (Petry et al., 2005a). Although magnitude affects efficacy (Petry et al., 2004), prize CM can engender equal benefits to voucher CM even when prize CM arranges for lower reinforcement magnitude (Petry et al., 2007a). We also found prize CM to be more cost-effective than voucher CM (Olmstead &Petry, 2009). Our next step relates to understanding how aspects of the prize reinforcement approach impact outcomes. We usually arrange for a 50 percent chance of winning a $1, $20 or $100 prize with each draw. A retrospective analysis (Ghitza et al., 2008) suggests probabilities of winning prizes impact abstinence in the short term, and our data indicate that probabilities of winning $20 and $100 prizes are most strongly related to abstinence during and after treatment. In addition, patients desire a greater variety of prize categories, and availability of more prize category options may improve outcomes. This will be the first prospective trial varying probabilities of winning and prize categories available. We will randomize 300 cocaine-dependent methadone patients to 1 of 6 conditions: (a) a control group, (b) a CM condition that arranges a 100 percent probability of winning a prize with each draw and has 3 prize categories, (c) a CM condition that arranges a 31 percent probability of winning and has 3 prize categories, (d) a CM condition that arranges a 100 percent probability of winning and has 7 prize categories, (e) a CM condition that arranges a 31 percent probability of winning and has 7 prize categories, or (f) usual prize CM with a 50 percent probability of winning from 3 prize categories. Magnitudes of reinforcement will be identical across conditions, but lower overall probability conditions arrange for greater chances of winning larger magnitude prizes. We expect that the new CM conditions will reduce cocaine use relative to the control condition, that 31 percent probability conditions will decrease drug use relative to 100 percent conditions, and that 7-prize category conditions will reduce drug use compared to 3-prize category conditions. In addition, the 31 percent/7-category condition is expected to be most efficacious and improve outcomes relative to usual CM. We will also evaluate effects on secondary outcome measures such as HIV risk behaviors and predictors of outcomes. Results will be instrumental for further developing prize CM to improve outcomes of cocaine-dependent methadone patients. PUBLIC HEALTH RELEVANCE: Prize-based contingency management (CM) is efficacious in improving outcomes, but little research to date has focused on the reinforcement parameters in prize CM and how they impact outcomes. These studies will systematically vary probabilities of winning prizes and the number of prize categories available to identify the most efficacious prize CM approach. The study will be conducted with cocaine-using methadone patients, as this group has significant drug use and related problems, and CM may be cost-effective in this population.